Recently, fuel cells have been receiving attention as highly efficient and environmentally friendly cells. Fuel cells typically generate electrical energy by causing hydrogen serving as a fuel gas to electrochemically react with oxygen in the air serving as an oxidant gas. As a result of the electrochemical reaction between hydrogen and oxygen, water is produced.
There are different types of fuel cells, such as phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells, and polymer electrolyte fuel cells. Among these, attention has focused on fuel cell systems employing polymer electrolyte fuel cells, which are advantageous, for example, in that they can be started up at ordinary temperatures and quickly. Such fuel cell systems are used as a power source for vehicles or other moving bodies.
When a fuel cell system is operated under a low-temperature environment such as outdoors in cold climates, the produced water may freeze in a gas flow path or elsewhere within the fuel cell. For this reason, a drying process in which scavenging is performed by passing an oxidant gas or the like through the fuel cell such that water remaining in the fuel cell is discharged when the fuel cell has stopped operation, has been employed. For example, Japanese Patent Publication No. JP 2006-79864 A describes that scavenging is performed by passing a fuel gas or an oxidant gas through the fuel cell upon stoppage of electric power generation of the fuel cell such that remaining water is discharged from the fuel cell.
On the other hand, a drying process in which the fuel cell is warmed by heating a coolant using a heater or the like, and conveying the heated coolant to the fuel cell using a coolant pump after the fuel cell has stopped operation, has been employed. Here, the heater, the coolant pump, and the like are connected to a secondary battery (rechargeable battery), and power is supplied from the secondary battery. However, because the discharge capacity of a secondary battery is limited, the drying process of the fuel cell may fail to be sufficiently performed due to, for example, running out of remaining capacity halfway through the drying process.